With more nutrients per calorie and square foot of growing space than any other food, leaf crops can be an invaluable addition to every yard or garden. As hardy as they are versatile, these beautiful, tasty vegetables range from the familiar to the exotic. Some part of this largely untapped food resource can thrive in almost any situation. Eat Your Greens by David Kennedy (New Society Publishers, 2014), provides complete instructions for incorporating these nutritional powerhouses into any kitchen garden.
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A constantly replenished wave of light leaves the surface of the sun, races across 93,000,000 miles of swirling space in less than nine minutes and lands on the tender green surface of a living plant. A few trillionths of a second later, the chlorophyll in the leaf has used that photon bit of energy to combine carbon, hydrogen, and oxygen from earth’s abundant air and water into sugar, the sweet fuel of life. From this simple sugar are formed complex sugars, starches, and fibers. Plants store the energy from the sunshine in their stems, roots, and fruits. Gardeners and farmers try to manage this biological solar energy collection operation in ways that benefit them. Simply climbing a hill gave me a useful perspective on this important undertaking.
From a hillside overlooking forests and corn fields in late spring, the forest appeared as a plush unbroken carpet of 50 shades of green, while the young corn looked like green lines marked across a sheet of brown paper. Clearly, the forest had more leaves basking in the sunshine than the corn. By late August, the verdant forest was looking down on a cornfield that had already produced all the corn it could and now held lifeless amber waves of grain drying in prime farmland. Yet this cornfield was the culmination of modern agricultural science — dependent on tractors, genetically modified seeds, herbicides, insecticides, and synthetic fertilizers — while the green forest was simply neglected and ignored.
An acre of forest has more surface area of green leaves more of the year than an acre in grain crops. This enables it to produce far more biomass, or living substance. The ratio of the surface area of green leaf to the surface area of the ground below it is called the Leaf Area Index (LAI). As a general rule, high LAIs correlate with high net productivity in any terrestrial ecosystem. (Aquatic ecosystems are usually powered by photosynthetic algae rather than leaves.)
Logic would suggest that an LAI above 1.0 is not possible because one square meter of leaf would intercept all of the sunshine falling on one square meter of ground. However, some ecosystems, such as pine forests, actually have LAIs as high as 10. Try reading something in the very shadiest spot in a park or a forest at midday. Despite a seemingly complete cover of tree leaves overhead, your eyes will still intercept enough sunlight to be able to read. Shade isn’t darkness. Some of the incoming photons bounce off the leaves back out into space; some pass directly through the thin leaves; and some bounce around until they find your eyes. Logic doesn’t appreciate how energetic, quick, and bouncy light energy is.
The ability of green leaves to capture the radiant energy of sunshine and convert it to food and fiber is the basis of life on Earth. The bulk of our food is currently grown in anti-forests: large, uniform plantings of annual grains and soybeans. Most of the advantages of forest over grain fields are a function of greater complexity. Forests have much more diversity of species, of plant sizes and types, and of animal, bacterial, and fungal communities. Complexity increases yield. A very simplistic example of this basic principle can be seen by intercropping corn and cowpeas. Two acres of intercropped corn and cowpeas will typically yield about one-third more than one acre in just corn plus one acre in just cowpeas. Forests extend this principle on every level. The complex interactions among different kinds of living beings in a forest enables more complete harvesting of sunlight and more efficient recycling of nutrients. This complexity not only allows forests to thrive without the fertilizers that drive our food system, it also builds in resilience that monoculture agriculture lacks.
Forests are amazing, but by now you may be wondering if I’ve overlooked a key point. While forests produce a surprising variety of foods that we could eat, their primary output is the cellulose and lignin in wood. We don’t eat wood. A patch of typical North American forest the size of an average home garden (about 600 square feet) would produce a disappointing amount of readily eaten food for a family. However, we can still improve the way we grow much of our food by employing some of the natural advantages that forests have over our grain fields. That is, if we learn to grow in three dimensions instead of two.
The most forest-like plants in the home garden are likely to be dwarf fruit and nut trees. Most tree leaves are too tough to be eaten, but there are a couple of exceptions. In the temperate zone, Chinese toon (Toona sinensis) and small-leaved linden (Tilia cordata) are two full-sized trees with edible leaves that stand out. In the tropics, moringa (Moringa oleifera), and chaya (Cnidoscolus aconitifolius) are smaller trees with spectacularly edible leaves. For practical reasons, edible-leafed trees are usually best kept pruned to a height that allows easy leaf harvest.
The home garden is generally not well suited for making good use of full size trees, except for shade. However, many of the forest advantages from taller plants and a higher leaf canopy can be simulated by growing climbing plants on trellises. Trellises are frames of any kind that provide support for a climbing or vining plant.
From the point of view of the plant, a trellis offers the opportunity to harvest sunlight above the crowd without the metabolic expense of building a stout trunk. Instead of diverting resources to building its own physical support, the climbing plant can simply attach itself to a trellis and invest more heavily in foliage, roots, transportation of nutrients, and reproduction. For the garden as an ecosystem, trellised plants act as make-shift deciduous trees, providing a wind break, partial shade, and evaporative cooling on hot summer days and losing their leaves to allow the more dilute sunlight of fall, winter, and spring to pass through (to power newly planted cool-weather greens).
From the gardener’s perspective, using trellises and climbers allows two to three times greater yield from the same square footage of garden. This allows the gardener to focus resources such as compost and water on a smaller area while harvesting sunshine over a greater area. It is often far easier to keep a few square feet below your trellis weeded, watered, and mulched than to tend to double or triple that area without trellises. Trellised plants also reduce the problem of contamination from soil pathogens splashed up onto leaves by rain. Trellises also provide convenient perches which attract many song birds to serenade the gardener. The birds benefit the garden by eating insects and leaving nutrient-rich droppings.
Most of the leaf vegetables that thrive on trellises are members of the bean and pea family (Leguminosae) or members of the pumpkin family (Cucurbitaceae). Among climbing legumes, the leaves of peas, common beans, yardlong beans, (Vigna unguiculata subsp. sesquipedalis), hyacinth beans (Lablab purpureus), scarlet runner beans (Phaseolus coccineus), rice beans (Vigna umbellata), and winged beans (Psophocarpus tetragonolobus) are sometimes eaten. Climbing members of the pumpkin family that have edible leaves include chayote (Sechium edule), squash, pumpkins, gourds (Cucurbita pepo, C. mixta, C. maxima, C. moschata), fluted pumpkin (Telfaria occidentales), bitter gourd (Momordica charantia), and bottle gourd (Lagenaria siceraria). All of these are multi-use plants that are more often grown for their fruit or seed rather than their edible leaves.
Other climbing plants with nutritious leaves that could be more widely eaten include grapes, vine spinach (Basella alba and B. rubra), and sweet potatoes. Grapes are often used in ornamental horticulture to create shaded arbors, and covered entryways and fences. Vine spinach as its name implies likes to climb whatever is nearby. A perennial in the tropics, it is normally grown as an annual in the warmer parts of the temperate zone. It won’t tolerate frost and grows slowly in cool spring weather, but when the weather warms, it wraps around any fence, pole, trellis, or tree and takes off.
Most varieties of sweet potatoes are better described as sprawlers than as climbers. Still, they can be grown over low trellises such as A-frames covered with sturdy fencing. Letting sweet potato plants sprawl over a low trellis helps produce bigger sweet potato yields by preventing the plant from rooting where the vine contacts the soil. These side, or prop, roots can draw energy away from the main root production.
Trellises can be built from a wide variety of materials. Most trellises have a rigid framework to support the weight of the plants and some sort of netting or mesh or fencing that enables the plant to grab hold. I have found cedar poles to make good supports and have nailed hog fencing to the cedar for plant holds. Steel reinforcing mesh for concrete (often called remesh) is another good option for trellises. It has a 6" × 6" steel wire mesh that is strong enough to support any plants, and the openings are large enough to reach through for easy harvesting.
Pre-built trellises can be bought from building supply and garden shops but they are generally expensive and better suited to ornamental landscaping than growing edible leaves. There is some work involved in building good trellises, so it is worth using materials that will hold up for at least a few years. Most people prefer not having pressure-treated wood in their food gardens because of possible leaching of toxic chemicals. Actually, the use of arsenic, by far the most troubling chemical in treated wood, ended in 2003 and was replaced by much safer ACQ (alkaline copper quaternary). While ACQ-treated wood is still not permitted in certified organic production, most experts consider it reasonably safe to use in the garden.
Cedar, locust, cypress, and a few other woods are naturally rot-resistant alternatives to pressure-treated wood, though they can be expensive and hard to find. Building with scrap or used wood and accepting that your wooden trellises will need to be periodically rebuilt is another option.
One of my favorite trellis systems is just six to eight bamboo poles arranged in a tepee. Lay the poles on the ground with the thick end of the bamboos even with each other. Six or seven feet from the bottom, tie them together with a rot-resistant twine and trim off any bamboo more than nine feet long. Then stand them up and spread each individual piece of the base of the bamboo out to make a cone about four feet in diameter and six feet high. (If you are cutting fresh bamboo, don’t trim all the side shoots flush. Leaving a bit of side shoot on the bamboo allows climbing plants to take hold easier.) When you cut a stalk of live bamboo, it won’t regrow. Lots of people have bamboo patches in their yards that need repeated thinning. They are usually happy to have gardeners do that thinning in exchange for the trellis material.
Any kind of bean or peas or vine spinach planted around the outside of this trellis will happily climb the bamboo. A great arrangement for the bamboo tepee trellis is a donut-shaped bed, made by creating a rim of raised, loosened soil by digging it from out of the center. Then fill the hollow in the center with mulch that will hold moisture and keep weeds from competing with the trellised plants. If you have a patch of bamboo or have neighbors who do, you should always have a supply to make more trellises from thinning the bamboo. They usually need to be replaced every two to three years.
Bamboo trellises are rarely strong enough to support the weight of gourd, pumpkin, and squash plants. Tripods of cedar poles with some cross pieces or heavy fencing work well for these plants. You can easily make a shady spot for kids to play or to hang a hammock under with these cedar pole trellises. When you add netting or fencing to a trellis, it is helpful to start it 6 inches or so above the ground so that you can easily weed and mulch the young plants. They will find the trellis.
The number of creative ways to build trellises for plants to climb is easily matched by the number of ingenious ways that plants have evolved to climb them. Various plants have modified their stems, branches, leaves, flowers, and even roots to aid in the process of climbing skyward. For example the pumpkin or gourd family (Cucurbitaceae) sends out long thin tendrils looking for something to climb. The plants employ a system of hormone controls to elongate the cells on one side of a tendril to move it slowly in a circle until it encounters resistance. When it makes contact, different hormones signal the tendril to wrap tightly around the support it has located. Finally, through a brilliant bit of botanical engineering, some tendrils are able to coil like two springs winding in opposite directions and joined midway between the plant stem and the newly found support. This creates a strong but flexible bond.
With vine spinach (Basella alba), on the other hand, the growing tip of the plant moves in a slow circle until it encounters a suitable structure for climbing, and then the main stem of the plant wraps tightly around it. Some climbing plants, such as grapes, need a little help. Growers will often use twist ties to hold the grape stems to the trellis until it grasps the idea. As a rule, it is good to use thick twine, rope, or wire to help plants climb because fine string and wire can cut into the stem, cutting off the circulation of nutrients as the plant gets heavier. Peas and beans are such good natural climbers that they will sometimes intertwine with their own stems making thick tangles of their vines — and in the process reduce the amount of sunshine they can harvest. Smaller openings in the trellis helps avoid this problem. Poultry netting fits the bill nicely.
Trees and trellises are not the only way to add dimension to your leafy garden. Plants can be grown in containers, and the containers can be raised on platforms, poles, fences, decks, stairs, or on roofs. They can also be hung by ropes or chains from eaves or overhangs. The foliage of plants such as sweet potato, vine spinach, Okinawa spinach, New Zealand spinach, and wolfberry can be visually compelling as it spills over the sides of a hanging container. Plants growing in hanging baskets near windows will progressively shade more of the window as the summer gets hotter.
One of the most basic ways to add dimension and complexity to your garden is by going down, not up. As discussed earlier, building deeper soil definitely expands the possibilities of any garden. Another measure that makes for a more interesting and ecologically complete garden is digging a small pond. It doesn’t need to be a formal water pond with a pump and waterfalls, as nice as those are. Just a depression in your garden lined with plastic and filled with water will quickly become home to frogs, crayfish, and be visited by toads, turtles, butterflies, skinks, salamanders, snakes, and birds. Not only will their presence make your garden a more interesting place to spend time, most of the creatures drawn to your pond will help control any insects eating your crops.
Building more dimension and complexity into your garden creates greater yields and more resilience. It brings in more life in all of its forms. This creates a spectrum of opportunities for the willing gardener to engage in an intimate ecosystem.
Reprinted with permission from Eat Your Greens: The Surprising Power of Home Grown Leaf Crops by David Kennedy and published by New Society Publishers, 2014.
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